With the recent advent of increased popularity of motorcycles, both as sports vehicles and vehicles for basic transportation, an interest in motorcycle sidecars has been renewed. The substantial increase in passenger and load-carrying capacity provided by a sidecar enhances the utility of the motorcycle. A sidecar also adds an element of stability, the lack of which might otherwise discourage would-be users or purchasers of motorcycles.
Unfortunately, a motorcycle with a sidecar attached is not as easily handled and as maneuverable as a motorcycle without a sidecar attached. This factor has been a principal detraction from sidecar use that has prevented an increase in popularity of sidecars to the extent realized by motorcycles. The difficult handling characteristics of a motorcycle with a sidecar attached are due primarily to the fact that such a vehicle is asymmetrical with respect to both its center of gravity and its aerodynamic characteristics. The center of gravity of a motorcycle is located along the elongate axis of the motorcycle extending between the front and rear wheels such that upon acceleration or deceleration, or upon going uphill or downhill, there is no tendency for the motorcycle to turn. Likewise, a motorcycle without a sidecar is aerodynamically symmetrical with respect to the elongate axes or axis of travel such that headwind force components tending to move the motorcycle to the left are balanced by equal forces tending to move the motorcycle to the right.
When a sidecar is added, typically by mounting it to the right side of the motorcycle, the center of gravity of the combined motorcycle and sidecar moves to the right of the motorcycle and is located somewhere between the wheels of the motorcycle and the sidecar, depending upon the respective loads carried by each. Due to the offset center of gravity, and thus the offset center of inertia, and due to the fact that drive is only applied to the rear wheel of the motorcycle, a tracking problem exists. For example, during acceleration, the combined vehicle tends to pivot about the center of gravity and turn right, which must be counterbalanced by the motorcycle rider turning the motorcycle wheel to the left. More important than acceleration forces, because of the usually greater time duration of wind forces than that of acceleration forces, the headwind force components tending to move the combined vehicle left and right, respectively, do not necessarily counterbalance one another such that a net force is often present tending to move the combined vehicle to the right. The need to apply continuous counterbalancing forces to prevent the combined vehicle from turning to the right can be extremely fatiguing for the driver of the motorcycle, and thus substantially detract from the desired to use the sidecar.
There have been basically two approaches to counter the tendency of the combined motorcycle and sidecar vehicle to move to the right: the provision of toe-in and the provision of leanout. Toe-in refers to the slight inward set of the sidecar wheel in relation to the wheels of the motorcycle. As would be expected, setting of the sidecar wheel so that it is directed to the left counteracts the aforementioned tendency of the vehicle to turn to the right. Leanout refers to the orientation of the motorcycle wheels with respect to vertical. Leaning the motorcycle to the left, away from the sidecar, creates a tendency for the vehicle to turn to the left, thus also counterbalancing the aforementioned forces tending to move the vehicle to the right.
While provision for leanout and toe-in adjustment have, to a certain extent, solved the tracking problem, partially because of the complicated nature of prior motorcycle sidecar mounting arrangements, the adjustments thereto needed to set a desired degree of leanout and toe-in have likewise been complicated and time-consuming. Such adjustments to known sidecar mountings can only be performed while the motorcycle and sidecar are stationary and various measurements can be made. Furthermore, because of the nature of known mounting arrangements, the adjustment of leanout often affects the toe-in adjustment, and vice versa, thus requiring alternate multiple adjustments to each. The precise manner by which the adjustment to leanout is made, of course, varies depending upon the make and type of motorcycle and sidecars, but a brief description of the complicated nature of the problem involved can be found in "Principles of Rigging" (a brief guide to setting up a sidecar) by Frank Thompson Zuch, Don Spaulding and R. L. Carpenter at 86, et seq., of the April 1973 issue of Cycle World. As pointed out in this article, in most cases only experimentation will divulge the optimum setting for leanout. Detaching the sidecar often results in the optimum setting being lost. Thus, the more complicated and time-consuming the adjustment procedure, the less likely the user will be willing to detach the sidecar once attached, which of course detracts from the versatility and user satisfaction which could otherwise be enjoyed.
More importantly, even in mounting arrangements in which the adjustment procedure has been somewhat simplified, such adjustments have always been static or fixed, and because of this have only met with partial success in solving the tracking problem. The adjustments can only be made when the vehicle is stationary, and once made, the adjustment mechanisms are locked into place and cannot be altered during transit. An optimum setting is selected by experimentation and according to the most likely road and driving conditions that will be encountered during travel according to the user's judgment.
For example, in the mounting arrangement shown in U.S. Pat. No. 1,461,759, the leanout may be adjusted, but only when the vehicle is stationary. The sidecar is partially secured to the motorcycle by two pivotal connectors adjacent the bottom of the sidecar to permit relative pivotal motion. The mounting further includes two elongate connectors which extend from the sidecar adjacent the pivotal connectors to points on the frame of the motorcycle vertically spaced from the pivotal connectors. While the motorcycle is oriented in the desired pivotal position, nuts on the ends of the elongate connectors are screwed tightly against opposite sides of the frame of the motorcycle. Tightening of the nuts rigidly secures the sidecar to the motorcycle and fixes the desired leanout of the motorcycle. A turnbuckle member extending from the sidecar adjacent the pivotal connectors to the motorcycle at a point thereon vertically spaced from the pivotal connectors is provided to make the leanout adjustment and to hold the motorcycle in the desired position while the nuts on the elongate connectors are tightened. For all practical purposes, the nuts on the elongate connectors cannot be loosened by the motorcycle rider during transit. Even if this were possible, to do so would render the mounting insecure, and for safety reasons the nuts should not be loosened during transit. The turnbuckle is ineffective to adjust leanout when the elongate connectors are tightly fastened to the motorcycle during transit.
The provision of toe-in, even with means to adjust it during transit, is insufficient to solve the tracking problem. If the sidecar wheel is toed in more than 3.degree., excessive tire wear results, and thus, for all practical purposed, 3.degree. is the maximum amount of toe-in which may be permitted. This limited range of permissible adjustment to toe-in is insufficient to solve the tracking problem for the wide range of operating conditions that may be encountered. Thus, if the tracking problem is to be resolved, it can only be done by altering leanout as the varying operating conditions may dictate.
While, because of the manner in which adjustments must be made to known mounting arrangements, the amount of leanout must be fixed, the conditions of wind speed, acceleration, and street and highway grades are constantly changing under normal driving conditions. A leanout adjustment for high speed highway driving when headwinds are maximum is completely inappropriate at a lower speed which might be necessitated. A setting for high speed will cause the vehicle to tend to turn to the left at low speeds. A setting which may be proper when a passenger is being carried will be improper when a passenger is not being carried unless ballast is provided. Gravitational forces acting on the vehicle when it is climbing a hill will tend to cause the vehicle to turn to the right, whereas those same gravitational forces when the vehicle is traveling down the other side of the hill will tend to make it go to the left. Likewise, acceleration will tend to make the vehicle turn right, and deceleration will tend to make the vehicle turn left. Another factor which normally cannot be taken into consideration when arriving at an optimum setting for leanout is the presence of side winds which may tend to cause the vehicle to turn either left or right.
Clearly, these and many varying conditions cannot all be served by a single "optimum" setting, and thus, no matter what the fixed setting may be, the motorcycle rider may frequently find himself "wrestling" with the motorcycle to maintain a straight course.